securities became very
complicated.
II. Why Did Banks Hold These Instruments?
Given that originators would have understood the deterioration of the underlying quality of
mortgages, it is surprising that they held on to so many of the mortgage-backed securities (MBS)
in their own portfolios. These were not just the low-rated equity portions that would have
signaled their faith in the packages, but also the high-rated tranches that found a ready market
around the world.
The amounts of MBS held seemed too high to be purely inventory. Some holdings could
have been portions of the package they could not sell, but then this would not explain why banks
held on to AAA-rated securities, which seemed to be the most highly demanded of mortgage
backed securities. The real answer seems to be that bankers thought these securities were
worthwhile investments, despite their risk.1 Investment in MBS seemed to be part of a culture of
1As the crisis developed, some banks bought AAA-rated tranches and sold lower quality
securities as a partially hedged bet on the further deterioration of the housing market. This came
back to haunt them as the AAA-rated portion deteriorated more than the low-rated securities.
5
excessive risk taking that had overtaken banks (see Raghuram G. Rajan, 2005; and Anil K.
Kashyap, Raghuram G. Rajan, and Jeremy C. Stein, 2008).
A key factor contributing to this culture is that, over short periods of time, it is very hard,
especially in the case of new products, to tell whether a financial manager is generating true
excess returns adjusting for risk, or whether the current returns are simply compensation for a
risk that has not yet shown itself but that will eventually materialize. Consider the following
specific manifestations of the problem.
A. Incentives at the Top
The performance of CEOs is evaluated based in part on the earnings they generate relative to
their peers. To the extent that some leading banks can generate legitimately high returns, this
puts pressure on other banks to keep up. Follower-bank bosses may end up taking excessive
risks in order to boost various observable measures of performance. Indeed, even if managers
recognize that this type of strategy is not truly value-creating, a desire to pump up their stock
prices and their personal reputations may nevertheless make it the most attractive option for
them. There is anecdotal evidence of such pressure on top management.2
B. Flawed Internal Compensation and Control
2Perhaps most famously, Citigroup Chairman, Chuck Prince, describing why his bank continued
financing buyouts despite mounting risks, said: “When the music stops, in terms of liquidity,
things will be complicated. But, as long as the music is playing, you’ve got to get up and dance.
We’re still dancing.” Financial Times, July 9, 2007.
6
Even if top management wants to maximize long-term bank value, it may find it difficult to
create incentives and control systems that steer subordinates in this direction. Given the
competition for talent, traders have to be paid generously based on performance. But, many of
the compensation schemes paid for short term risk-adjusted performance. This gave traders an
incentive to take risks that were not recognized by the system, so they could generate income
that appeared to stem from their superior abilities, even though it was in fact only a market-risk
premium. The classic case of such behavior is to write insurance on infrequent events such as
defaults, taking on what is termed “tail” risk. If a trader is allowed to boost her bonus by treating
the entire insurance premium as income, instead of setting aside a significant fraction as a
reserve for an eventual payout, she will have an excessive incentive to engage in this sort of
trade. Indeed, traders who bought AAA MBS were essentially getting the additional spread on
these instruments relative to corporate AAA securities (the spread being the insurance premium)
while ignoring the additional default risk entailed in these untested securities.
This is not to say that risk managers in a bank are unaware of such incentives. However,
they may be unable to fully control them, because tail risks are by their nature rare, and therefore
hard to quantify with precision before they occur. While they could try and impose crude limits
on the activities of the traders taking maximum risk, these traders are likely to have been very
profitable (before the risk actually is realized), and such actions are unlikely to sit well with a top
management that is being pressured for profits.
III. Short-Term Debt
Given the complexity of bank risk-taking, and the potential breakdown in internal control
processes, investors would have demanded a very high premium for financing the bank long
term. By contrast, they would have been far more willing to hold short-term claims on the bank,
7
since that would give them the option to exit -- or get a higher premium -- if the bank appeared to
be getting into trouble. So, investors would have demanded lower premia for holding short-term
secured debt in light of potential agency problems at banks (as shown in Douglas W. Diamond
and Raghuram G. Rajan, 2001).
From the banker’s perspective, a certain sense of confidence that any troubles were far away
(which is what made them take on tail risk), would have made financing with short-term debt
claims much more attractive to the banks than issuing long-term claims. Clearly, banks should
have been worried about the possibility that they could become illiquid and incapable of rolling
over financing. Douglas W. Diamond and Raghuram G. Rajan, 2008, show formally that the
incentive of levered institutions to become more illiquid increases with expectations that future
interest rates would be low. With global savings pouring in, and with the Federal Reserve
emphasizing its willingness to pump in liquidity and cut interest rates dramatically in case of a
sharp downturn (the so-called “Greenspan Put”), it is not surprising that banks were willing to
take illiquidity risk.3
The more general point is that in good times, short-term debt seems relatively cheap
compared to long-term capital and the costs of illiquidity remote. Markets seem to favor a bank
capital structure that is heavy on short-term leverage. In bad times, though, the costs of
3This is why Diamond and Rajan, 2008, argue that regulators may want to raise interest rates
more than strictly necessitated by current economic conditions in good times, so as to offset the
incentive for banks to take on illiquidity when they know it will cut rates sharply in bad times.
8
illiquidity seem to be more salient, while risk-averse (and burnt) bankers are unlikely to take on
excessive risk. The markets then encourage a capital structure that is heavy on capital.4
IV. The Crisis Unfolds
Given the proximate causes of high bank holdings of mortgage-backed securities (as well as
other risky loans, such as those to private equity), financed with a capital structure heavy on
short-term debt, the crisis had a certain degree of inevitability. As house prices stopped rising,
and indeed started falling, mortgage defaults started increasing. MBS fell in value, became more
difficult to price, and their prices became more volatile. They became hard to borrow against,
even short term. Banks became illiquid, the canonical example being Bear Sterns, which was
taken over by JP Morgan in March of 2008.
The Federal Reserve opened new facilities that allowed banks to borrow against illiquid
positions. But as more banks tried to sell out of their positions, prices plummeted